The present invention relates generally to an optical read/write device for writing and reading data to and from an optical recording medium, and to an optical head incorporated in such device, and, in particular, to a device for use in writing and reading data by means of a beam of radiant energy transmitted to and from a magneto-optic recording medium.
In order to understand the background of the invention, reference is first made to FIG. 1 wherein a conventional optical head of an optical magnetic read/write device, generally indicated at 1600, is depicted. A semiconductor laser 1601 emits a beam of light 1620 which is directed through a collimating lens 1602. Collimating lens 1602 produces a collimated laser beam 1620. Beam 1620 is directed through a beam splitter 1603, through an objective lens 1604 and onto a magneto-optic recording medium 1605. Light reflected from magneto-optic recording medium 1605 is transmitted back through beam 1603 and through a half wave length plate 1606 and a polarizing beam splitter 1607 which divides the reflective beam of light into a first light beam 1622 and a second light beam 1624.
Light beam 1622 passes through a first optical detection system, generally indicated as 1626. Light beam 1622 first passes through convex lens 1608 then a cylindrical lens 1609 where it is projected onto a quadrant photo diode 1610 which a produces synthetic signal in response thereto. Light beam 1624 passes through a second optical detection system, generally indicated as 1628. Optical detection system 1628 includes a convex lens 1611 and a photo diode 1612. Light impinging on photo diode 1612 produces a signal. An optical magnetic read signal is obtained by producing a signal representing the difference between the signal produced by optical detection system 1628 and the synthetic signal produced by optical detection system 1626.
In accordance with a method known in the art as illustrated in Lee, "Optical Technology For Compact Disc Pick-ups", Laser and Optronics Vol. 5, No. 9, September 1987, a prepit signal which is modulated by the light strength of received light beams and a track error signal which is modulated by the wobbling pit are obtained as a function of the synthetic signal produced by the first optical detection signal 1626 and the signal produced by the second optical detection system 1628.
Reference is now made to FIG. 17 in which a signal processing circuit constructed in accordance with the prior art is depicted. A photo diode 1701 provides an input to a pre-amp 1703. Pre-amp 1703 converts the current input into a corresponding voltage output signal. A quadrant photo diode 1702 provides an output to four respective pre-amps 1704, 1705, 1706 and 1707 from each respective quadrant of quadrant photo diode 1702 to accomplish the current voltage conversion. A first adder 1708 receives an input from preamps 1704 and 1706. A second adder 1709 receives inputs from preamps 1705 and 1707. A third adder 1710 receives an input from adder 1708 and an input from adder 1709. An op-amp 1711 also receives an input from adders 1708 and 1709 to produce a focus error signal at an output 1716. An op-amp 1713 receives an input from pre-amp 1703 and adder 1710 to produce a magneto-optical read signal at an output 1714. An adder 1712 receives an input from pre-amp 1703 and adder 1710 to produce a prepit signal and track error signal at an output 1715.
Such conventional optical head and magnetic optical read/write devices have been less than satisfactory. The conventional devices require five amplifiers having low noise and broad band capabilities requiring complex processing circuitry resulting in an optical system which is very complex including a very large optical head. Additionally, because the magneto-optical signal reading system is not symmetric, the magneto optical reading signal tends to deteriorate due to the unbalance of the phase properties of the processing circuit. Additionally, the conventional optical heads and magneto optical processing systems do not lend themselves to high speed use.
Accordingly, it is desired to provide a miniaturized optical head for use in a magneto-optical read/write system which overcomes the shortcomings of the prior art and which achieves the objects and benefits associated with a less complex magneto-optical read/write system.